1. Field of the Invention
This invention relates to a photolithography technique in a manufacturing process of a semiconductor device, and more particularly, to a manufacturing method of a polysilicon film with rough-surface.
2. Description of Related Art
The technique of the photolithography is a very important step in the manufacturing process of the semiconductor device. The basic steps for the photolithography process include steps of coating, exposure, and developing. The step of exposure almost uses light as the medium for transferring of the pattern of a mask. As to reasons for effecting the ultimate resolution of the exposure, it depends on wavelength of the light source employed. Generally, the shorter the wavelength of the light source is, the smaller the resolution of the exposure is.
In the commercial applications of the photolithography technique, the wavelength of the light source used in common is so-called G-line and I-line. The wavelength of the G-line is 4360 .ANG., and the wavelength of the I-line is 3650 .ANG.. Another light source of a krypton fluoride laser provides a deep ultra-violet ray with 2480 .ANG.. The new light source can satisfy demands for the next-generation 64M bits DRAM. Therefore, accompanying the continually diminishing of the design rules, the wavelength of the light source used in photolithography process has to be decreased at the some time.
However, when a shorter wavelength of the light source is selected, the strength of refraction of the thin film will relatively increase in the exposure process of the photolithography. It causes the critical dimension (CD) having a large swing, i.e., changing to large degree in the proceeding of manufacturing process, it also leads to incorrect pattern transfer of the photolithography process.
Referring to FIG. 1A.about.1E, show cross-sectional views depicted from selected process stages of a conventional procedure used in solving this problem. At first, referring to FIG. 1A, shown a substrate 100. A thin film 101 is formed over the substrate 100 and the thin film 101 is intended for proceeding of the photolithography process. The thin film 101 is made of any kind of materials which are necessary for defining patterns in photolithography process, for example, a polysilicon layer or tungsten silicide.
Next, referring to FIG. 1B, the thin film 101 is coated with an anti-reflection layer (ARL) 104. The anti-reflection layer 104 is made of mineral materials, which can absorb a portion of the light and decrease the reflection coefficient of the thin film while proceeding the manufacture process. The method of decreasing the reflection coefficient of the thin film can be performed by, for example, adjusting the thickness of the anti-reflection layer 104. The method also can be performed by adjusting the features of the anti-reflection layer 104, for example, by changing the reflective index or degree of the absorption, of the anti-reflection layer 104, to a destructive interference degree. By the above-mentioned adjusting methods, the critical dimension (CD) is maintained in a stable condition, by which the pattern transfer of the photolithography process can avoid incorrectness.
After that, referring to FIG. 1C, the anti-reflection layer 104 is defined by photolithography and etching process using a photoresist layer as a mask and is changed into a anti-reflection layer 104a. Next, referring to FIG. 1D, by using the anti-reflection layer 104a as a hard mask the thin film 101 is etched and changed into a thin film 110a. Finally, referring to FIG. 1E, the anti-reflection layer 104a is eliminated and the desired thin film is formed.
According to the conventional method, using the anti-reflection layer 104 to decreasing the reflection coefficient of the thin film is performed by an another complex method. That is, the device has to be moved to another machine from the original machine. It causes the process more complex and, for forming the anti-reflection layer, the original thin film 101 possible to be damaged in the manufacturing process.
Furthermore, the material of the anti-reflection layer 104 is not conductive and is quite different from the original thin film 101, therefore, the thin film 101 requires being defined after the anti-reflection layer. That is, the transfer pattern of the thin film 101 is completed after the transfer pattern of the anti-reflection layer 104. Moreover, when the transfer pattern of the thin film 101 is performed, the defined anti-reflection layer 104 has to be eliminated. Therefore, the conventional method, by forming a anti-reflection layer to decrease a reflection coefficient of the thin film, makes the procedure of the manufacturing more complex. Furthermore, if the residual anti-reflection layer 104 is not eliminated completely, the resistance of the device will increase, even forming open condition. These defects cause the yield rate of the manufacturing reduced.